if you have the budget,buy a 12 - 13" (the widescreen 12's are nice).
i'm thinking lattitudes ( d420 is my favo) or any brand for that matter.
If you buy a discrete laptop backpack, perhaps attached with some bubblewrap on the inside of the laptop-holding dept (yes,i went there
), you could slap that backpack around like you don't care, certainly not giving away there is a laptop in there.
Its more the bag than the laptop anyways.
Sure , i had a 17" widescreen before my lattitude for going to school,it fitted nicely in my bag.
There were no problems,but you can't swing it around ,and its heavier